Arrangements for feeding blood to a vascular access and/or for taking blood from a vascular access, via a line, are generally familiar. Such arrangements are distinguished by the fact that the blood is fed to the vascular access, such for example as an access to a vein or artery, or is taken away from the vascular access, via a line. Arrangements of this kind are known in the form of, for example, infusion or transfusion arrangements.
The known pieces of apparatus for extra-corporeal blood treatment, for the purposes of hemodialysis, hemofiltration or hemodiafiltration for example, are also arrangements in which blood is fed to a vascular access via a line and blood is taken from a vascular access via a line.
In the known methods of treating blood, such as for hemodialysis, hemofiltration or hemodiafiltration for example, the patient's blood is conveyed through an extra-corporeal blood circuit which includes the means for treating the blood. The extra-corporeal blood circuit is generally fitted with a protective system which constantly monitors the arterial and venous pressures in the circuit. The purpose of this monitoring of pressure is to detect various complications which may occur during the extra-corporeal blood treatment. Among the possible complications is a faulty vascular access which is attributable to, for example, the needle slipping out or being drawn in.
When a faulty vascular access is found, the known protective systems as a rule make provision for the blood pump for pumping the blood in the extra-corporeal blood circuit to be stopped, a tube clamp on the venous blood line of the extra-corporeal circuit to be closed and an audio or visual warning signal to be given. By this means, the blood treating apparatus is changed to a state which is safe for the patient, but one which results in the therapy being interrupted.
Methods and arrangements for monitoring an extra-corporeal blood circuit which are based on monitoring of the pressure in both the venous and the arterial segments of the extra-corporeal blood circuit are known for example from German Patent Application Publication DE 10 2006 032 815 A 1 and European Patent Application Publication EP 0 995 451 A2.
A further complication which may occur in the course of, for example, extra-corporeal blood treatment is an injury to the vascular access which results in bleeding into the surrounding tissue, something which is also referred to as perivascular bleeding. Because cases of perivascular bleeding produce only a very slow rise in pressure in the line running to the puncture needle or in the puncture needle itself, the detection of perivascular bleeding is a problem in practice. If the pressure in the line or needle is still well below the limiting value of pressure at which the known pressure-monitoring arrangements respond, the rise in pressure per unit of time, which is only small, is not noticed at first, even though more and more blood is continuously bleeding into the tissue at the time and builds up there when this happens, as a result of which more and more harm is done to the patient. A considerable amount of time therefore passes, in which blood bleeds into the tissue undetected, until the limiting level of pressure is reached.
Other methods and arrangements for detecting a vascular access which is not in good order and which are based on the monitoring of pressure signals are known from, for example, U.S. Pat. No. 4,530,696, U.S. Pat. No. 5,423,743 or U.S. Pat. No. 4,846,792. Known from European Patent EP 0 817 653 B1 is an arrangement which is fitted to a puncture needle to detect the entry of blood into the needle. The entry of blood when the blood vessel is pierced is detected by measuring a rise in pressure by means of a pressure sensor. With the known arrangement, it is even possible for the piercing of the opposite wall of the vessel to be detected by means of the drop in pressure which occurs when the opposite wall of the vessel is pierced.
The object underlying the present invention is to specify a method which, when blood is being fed to a vascular access via a line and/or blood is being taken from a vascular access via a line, and in particular in extra-corporeal blood treatment, makes it possible for perivascular bleeding to be detected quickly with relatively high safety and reliability. A further object of the present invention is to provide an arrangement for detecting perivascular bleeding which, when blood is being fed to a vascular access and/or blood is being taken from a vascular access, and in particular in extra-corporeal blood treatment, allows perivascular bleeding to be detected quickly with relatively high safety and reliability. As well as this, it is also an object of the present invention to specify an extra-corporeal blood treating apparatus having an arrangement for detecting perivascular bleeding which detects perivascular bleeding quickly with relatively high safety and reliability.
These objects are achieved in accordance with the present invention by virtue of the features of features described herein.